Assistance with the surgical treatment of cancer is currently based on several techniques.
In a first type of technique called “pre-operative imaging techniques”, before the operation the surgeon creates an image of the tissue area to be treated in order to locate, as well as possible, the tissue parts to be excised.
Pre-location of the tumour, by means of x-ray tomography or of IRM is used, for example, to obtain the precise anatomical topography of the tumorous volume and thus to choose the most appropriate surgical approaches. When coupled with mechanical stereotaxic or optical guidance, preoperative location leads to more narrowly defined and therefore less traumatising access paths, especially in the case of deep lesions.
In neurosurgery, this technique can be complemented by the use of a functional isothermal remanent magnetisation (IRM) imaging appliance, which is used, before the surgical procedure, to precisely identify the functional cerebral zoned located close to the tumour. On the basis this information, the surgeon is then able to optimise the extent of the zone to be excised while also minimising the risks of postoperative morbidity.
Preoperative imaging techniques have allowed the introduction of surgical procedures that are more precise and less invasive.
However, these techniques have limits in terms of performance and ergonomic design. In particular, these techniques are ill-suited to operations requiring location of small tumours and their metastatic disseminations if any.
In addition, the displacement of the tissue during the surgical procedure (in particular in the brain) often renders obsolete the location of lesions effected before the operation.
According to a second type of technique, the surgeon takes tissue samples during the operation, and these samples are analysed extemporaneously, so as to ensure the quality of the operating procedure of the surgeon.
These techniques, which rely upon precise anatomopathological diagnosis of the tissue samples have the advantage of being very reliable.
Such techniques are very costly however.
In addition, the time necessary to obtain a diagnosis from the samples may sometimes significantly increase the time of the surgical procedure.
Given the drawbacks associated with the preoperative imaging techniques and the tissue sampling techniques, a third type of technique called “preoperative techniques” has appeared. These techniques employ monitoring tools that are suitable of working in an operating suite, and thus of supplementing the outside imagers by helping the practitioner to determine the margins of a tumorous resection or a biopsy more precisely and in real time.
Two families of preoperative technique are currently under study. The first family of techniques, called “anatomical preoperative techniques”, is based upon standard anatomical imaging systems, such as optical endoscopy systems, ultrasound echography, x-ray tomography or isothermal remanent magnetisation (IRM). The second family of techniques, called “functional preoperative techniques”, are based upon the detection of signals emitted by the tissue by virtue of miniaturised systems. The signals are particles or radiation emitted by radioactive tracers or fluorescent molecules present in the tissue and specific to the tumorous lesions looked for.
According to the anatomical preoperative techniques, in order to guide his actions, the surgeon uses an anatomical imaging appliance identical in principle to those used in clinical diagnosis departments but whose characteristics, in terms of dimensions and ergonomy, have been adapted for use in operating suites.
As a complement to preoperative examination, low-field IRM and the x-ray tomography are used mainly in the operating suite in order to correct location errors associated with the displacement of the tissue during the procedure and to guide the biopsy procedures. The anatomical imaging systems are in fact used to repeat, in real time, the images created before the procedure and, as a consequence, to monitor the distortion of anatomical structures in real time. Evaluation of the preoperative IRM for surgery of the gliomas has thus shown that these techniques allow one to improve identification of the extent of the tumorous resection in relation to the procedures in which only stereotaxic guidance based on preoperative images was used.
Ultrasound echography is also used in the operating suite to assist with the surgical treatment of tumours. This technique has the advantage of being a lot less expensive and costly to put in place than low-field IRM or x-ray tomography. The principal field of application of preoperative ultrasound echography is the location of non-palpable breast tumours and tumours of the liver. More generally, this technique is particularly adapted for the precise location of deep lesions.
According to the functional preoperative techniques, the surgeon uses a miniaturised detection device that is suitable for detecting radioactive tracers or light radiation specific to the histology or the physiological or metabolic behaviour of the tumorous lesions looked for. Since the function of an organ is often disrupted before its structure, these techniques are therefore theoretically more sensitive and specific than anatomical preoperative techniques in order to distinguish the healthy tissue from the cancerous tissue.
It is thus possible to optimise identification of the extent of the tumorous resection beyond the margins identified by the preoperative examination and without having to wait for the results of extemporaneous examinations of tissue samples.
These techniques can also be used to improve the diagnosis precision of biopsies by guiding the surgeon to relevant regions of tissue to determine the histological nature of the tumour.
In general, miniaturisation of the detection devices used also leads to easier application of the functional preoperative technique in the operating suite, since it only slightly modifies the surgical protocol in relation to the more expensive and restrictive anatomical preoperative techniques.
Various counting or functional preoperative imaging devices have been developed. Some are even currently commercialised. However these devices are notable for several instrumental and methodological limits. Since there currently exists no system for functional preoperative imaging that allows the location and the simultaneous excision of the tumorous tissue. The current protocols combine two different tools which are used sequentially—the detection system (probe, microscope) and the excision tool (ultrasound aspiration device or electric lancet). This dissociation leads to correlation errors between the position of the tumour identified on the image and its actual position in the wound, and therefore reduces the precision of the excision procedure, in particular in the absence of anatomical location. The other limit of the functional preoperative devices relates their specific natures (associated with the tracers used) that is not total and therefore results in a non-negligible number of false negatives.